Good question. I hope someone has a good answer. +1
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RobustoNov 30 '10 at 19:21

The question of which dictionary applies to a community (the question in the body) is different from which dictionary people turn to (the question in your title). Which one are you actually interested in? If it's the latter, then something like Google Trends (or book sales) seems the only way towards an answer, while if it's the former, there may be more authoritative answers.
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ShreevatsaRDec 11 '10 at 12:20

I would disagree. If you search for an online dictionary in the US, the Oxford English Dictionary that comes up is American. For online usage, the Cambridge Dictionary is the definitive British English dictionary. Oxford is now universal and regional.
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Jimi OkeDec 13 '10 at 0:04

@Jimi Oke: Even if there is a regionalized OED for American English, Gomez's method shows that Merriam Webster's is much more popular. Similarly, the OED is slightly more popular in the UK than the Cambridge Dictionary.
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EricDec 13 '10 at 10:16

The languages vary tremendously in both spelling and meaning, in some areas (such as cookery and food) more than others. The language is relatively common and certainly in the modern age with the perfusion of international television, we understand many of the differences orally due to exposure. This does not mean we see the spellings everyday, or have a firm grasp of the usage differences, particularly when obscure.

Using a dictionary tailored for another region than your own is unwise at best. The languages are not the same, though are mutually corruptive.